Epidemiology and Ecology of Bacillus cereus biovar anthracis in Taï National Park, Côte d’Ivoire ; Epidemiologie und Ökologie von Bacillus cereus biovar anthracis im Taï Nationalpark, Elfenbeinküste

Sudden death was observed in chimpanzees and gorillas in Côte d’Ivoire (Taï National Park) and Cameroon (Dja Reserve) in 2001 and 2004 and the causative agent was identified as a before unknown Bacillus anthracis-like bacterium designated Bacillus cereus biovar anthracis (Bcbva) (1, 2). Bcbva combines the chromosomal background of B. cereus with the virulence plasmids of B. anthracis and was shown to be as virulent as B. anthracis in small animal models (3). As part of an ongoing long-term study in Taï National Park (TNP), autopsies on all available deceased wildlife were performed and environmental samples were collected. Bcbva positive samples dated back up to 1991 and Bcbva was identified as a continuous cause of death for a number of large mammal species (4). The aim of the present study was to investigate the epidemiology and ecology of Bcbva in its natural rainforest habitat in TNP using a broad array of phylogenetic and serological methods. Bacterial isolates could be retrieved from various sample types (tissue samples, bones, carrion flies) and 178 whole Bcbva genomes were derived covering a period from 1996 to 2014. SNP-based phylogenomic analysis in a Bayesian statistical framework revealed that Bcbva chromosomes had measurably evolved over this time span. This allowed us to determine that the median time to their most recent common ancestor (tMRCA) was 146 years (95 % highest posterior density (HPD): 70-237) and that 0.2 new mutations are introduced in average per Bcbva chromosome/year. Bayesian Markov Chain Monte Carlo (BMCMC) analyses were run under several demographic models. No model outperformed a constant population size model, suggesting Bcbva population size did not vary much over this period. To further inform the latter, in vitro experiments were performed determining the whole genome mutation rate of Bcbva, which was shown to be comparable to the in vitro mutation rate of B. anthracis. Comparison of Bcbva evolutionary rate and in vitro mutation rate approximated hypothetical Bcbva activity ...